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Chemical vapor deposition growth
of carbon nanotubes:
characterization and applications
University of L’Aquila - Italy
Maurizio PassacantandoDipartimento di Fisica, Università degli Studi dell’Aquila
Structure of SWCNTs
Diameters: 0.6 - 2.0 nm
Length: 1 - 103 μm
Chiral Vector
Ch = nâ1 + mâ2
n2m
n3tan 1-
Chiral Angle
h
t
Cad
2
1
22 )nmn(m 3
CC-
Diameter
Electronic structure of SWCNTs
Energy dispersion relations for 2D graphite Wave vector k for 1D CNTs in 2D Brillouin
zone of graphite (hexagon) as bold lines for
(a) metallic and (b) semiconducting CNTs
CNTmetallic
semiconducting
n − m = 3q
n – m ≠ 3qq
Density of states of SWCNTs
dEEkE
dk
kdEN
TED
N
1
)()(
1
2)(
1D density of states in units of states/C-atom/eV
Quantization of the wave vector along the circumferential direction leads to a
density of states characterized by sharp van Hove singularities.
semiconductor side metal side
Structure of carbon nanotubes (CNTs)
Diameters: 0.6 - 2.0 nm
Length: 1 - 103 μm
Single-Wall Carbon Nanotubes (SWCNTs)
Multi-Wall Carbon Nanotubes (MWCNTs)
Diameters: 2.0 - 100 nm
Length: 1 - 103 μm
More complex is the behaviour for
multi-wall carbon nanotubes
(MWCNTs)
because of interactions
between adjacent layers
Sample Preparation:
Chemical Vapor Deposition (CVD)SubstratesCatalyst filmGrowth
Characterizations:
Scanning Electron Microscopy (SEM)X-ray Photoelectron Spectroscopy (XPS)Electron Energy Loss Spectroscopy (EELS)Raman Spectroscopy Transmission Electron Microscopy (TEM)
Applications:
NanolytographyNanomanipulationI-V measurementsGas SensingPhotoconductivityField Emission
Outline
Ni or
Sample Preparation:
• Catalyst particle in
molten state absorbs
carbon in vapor form
(a) to form an alloy (b).
• As the particle
becomes saturated
with carbon, a solid
CNT begins to extrude
from the particle.
• The final location of the
catalyst particle
defines tip grown (c) or
root grown (d) CNTs.
Stig Helveg et al.
Nature 427, 426 (2004)
Catalyst Film:
Ni or Fe
Substrate
Substrate:
Silicon, Glass, Aluminum, Copper, …
Clusterization of catalyst film:
Annealing in H2 or NH3
CNTs growth:
C2H2 : H2
C2H2 : NH3
Sample Preparation:
Vertical CVD
Pumping
System
Heater
Power Supply
HV Power
Supply
Vacuum
Gauge
C2H2 H NH3
V1
V2
V3
V4 V5V6
Mass
Flow
50 sccm
Temperature
Control
Mass
Flow
100 sccm
Mass
Flow
200 sccm
Sample Preparation:
Horizontal CVDSample Preparation:
DT
New CVD reactor
TOP
VIEW
Synthesis of CNTs:
Chemical Vapour Deposition (CVD)
T= 500 °C
T= 700 °CCharacterizations: SEM
XPS
1000 800 600 400 200 0
0
20000
40000
60000
80000
100000
120000
C (KVV)
O(1s)F(1s)
C(1s)
c/s
Energia di legame (eV)
0 10 20 30 40
0.00
0.02
0.04
0.06
0.08
0.10
0.8
1.0
HOPG
CNT old growth
CNT new growth
Inte
nsity (
arb
itra
ry u
nits)
Energy Loss (eV)
-plasmon
EELS
Ep=1000 eV
EELSRaman
1000 1200 1400 1600 1800
Inte
nsity (
arb
itra
ry u
nits)
Raman shift (cm-1)
D peak G peak
Characterizations:
TEM: Morphology
CNT growth at 500 °C
135 nm
• Elongated structures (l ~ 50 – 150 nm, d ~ 30 – 50 nm)
• The structure is more similar to a filled cylinder than to a tube
• At the edges round particles are visible with diameter 5 – 20 nm.
Characterizations:
Unfiltered Energy filter Carbon edge Energy filter Nickel edge
The particles (d~20 nm) are made of Nickel and are located close the apex
of the structures.
TEM: Chemical Composition
CNT growth at 500 °C
Characterizations:
The external shells are not well graphitized
Catalyst grains
Around the grains there is a crystalline core
TEM: Crystalline Structure
CNT growth at 500 °C
Characterizations:
• Tubes with hollow interior (l ~ micron scale, dext ~ 10 – 30 nm).
• Several tubes look bended
• At the edges particles are visible with diameter 5 – 20 nm.
• Inclusions of particles are also present along the tubes.
TEM: Morphology
CNT growth at 700 °C
Characterizations:
Unfiltered Energy filter Carbon edge Energy filter Nickel edge
TEM: Chemical Composition
CNT growth at 700 °C
Characterizations:
Unfiltered Energy filter Nickel edge
Long Nickel inclusions (defects) are observed
TEM: Chemical Composition
CNT growth at 700 °C
Characterizations:
• Outer diameter: 15 – 25 nm
• Inner diameter: 5 – 10 nm
• Average # of tubes: 10 – 15
TEM: Crystalline Structure
CNT growth at 700 °C
Characterizations:
TEM: Tubes Capping
CNT growth at 700 °C
Characterizations:
In proximity of the catalyst the
carbon is highly graphitized Uncapped Tubes: cores
TEM: Particle Inclusion
CNT growth at 700 °C
Characterizations:
Self-patterned Growth: Black & White
BlackNi catalyst
Whiteno catalyst
Binding Energy (eV)
Inte
nsit
y (
arb
itra
ry u
nit
s)
Inte
nsit
y (
arb
itra
ry u
nit
s)
Energy Loss (eV)
Inte
nsit
y (
arb
itra
ry u
nit
s)
Raman Shift (cm-1)
Applications:
Nanolithography
&
design for the CNTs growth
GINT collaboration
Applications:
lift-off of Nichel film (3 nm)
Silicon
Silicon
GDSII mask design
Electron beam exposure
Silicon
After developing
Nichel film deposition
Silicon
Aceton bath
Applications:
GDSII mask design
Applications:
Applications:
Applications:
Applications:
CNTs
CNTs
CNTs
CNTsCNTs
CNTs
Selective Chemical Vapour
Deposition growth of carbon
nanotubes on submicrometric Ni
patterns fabricated with Scanning
Probe Nanolithography
Digital Instruments D5000 Microscope
(Nanoscope IV controller) using
commercial silicon tips (frequency
range 310-370 kHz) scanned by
means of a Veeco Nanoman closed
loop XY head.
Applications:
(a) 18.0 μm × 2.5 μm AFM micrograph of 13 nm PMMA
on SiO2 substrate after nanoindentation.
(b) AFM micrograph of the same area of panel (a) after
deposition of 3 nm of Ni and subsequent lift-off of
resist.
(c) Height profile of the written line on PMMA (see
panel (a)).
(d) Height profile of a Ni stripe, evidenced in panel (b).
(a-c) 5 μm × 3 μm AFM and SEM
(60000x) micrographs of three Ni
stripes before (a-b) and after (c)
growth of CNTs.
M. Passacantando et al., J. Appl. Phys. 101, 066101 (2007)
Applications:
Applications:
Manipulation and electrical characterization of
carbon nanotubes by using
nanomanipulators inside SEM
CNT metal contact
M M
CNT
SiO2
Silicon
Schematic picture of CNT distortion across metallic pads
... influence on the CNT intrinsic electronic transport properties
CNT structural distortions ...
CNT on surface/metallic pads:
It is therefore advantageous to performs electrical measurement on CNTs inthe free space, and it is also desirable to have the possibility to manipulate acharacterized carbon nanotubes into predetermined position for deviceconstruction.
CNT 3D manipulation in free space (!)
Applications:
• no structural distortions
• no post-processing process (lift off, metallization, etc...)
Nanomanipulation under Scanning Electron Microscopy:
+
nanomanipulator
SEMCNT manipulation@NIST
Applications:
CNT 3D manipulation in free space
• Viewing and placement of probe contacts at specified locations along a CNT.
• Three dimensional freedom=all the aspects of the investigated CNT can be explored.
• No ambiguities related to the interpretation of the results of electrical and mechanical experiments.
CNT manipulation under SEMApplications:
•MWCNT manipulations under SEM
• MWCNT as grown on Ni wire by CVD
• I-V characterization of MWCNT
• I-V characterization of CNT/CNT
junction
“Nanowelding”via
Electron Beam Induced
Deposition
Applications:
Experimental
• MM3A-nanoprobe system (Kleindeik Company)
• Scanning Electron Microscopy (ZEISS, LEO 1430)
• The manipulators are coupled with a Keithley-236 electrometer to
perform electrical current-voltage (I-V) measurements.
Approaching CNT...
A
Ni wire
VW tip
Schematic of the I-V apparatus
Applications:
Experimental
MWCNT grown on Ni template:
low contact barrier at the Ni/CNT interface
theimprovinginirradiationBeamElectrontheofeffectThe…W/CNT contact has been investigated …
Applications:
I-V vs Electron Irradiation
1) Approaching CNT protruding from the Ni tip
2) I-V acquisition
3) Electron beam irradiation of the contact area (10 keV, 10 min)
4) I-V acquisition after each irradiation cycle
Approaching CNT Electron beam irradiation of the W/CNT contact area
Irradiated area
Applications:
Ni tipW tip
Applications:
Applications:
Applications:
CNT W Tip CNT W Tip
Contact resistance
I-V vs Electron Irradiation: RESULTS
• Resistance at W/CNT junction:
• Contact area
• nature of metal electrode
• CNT/metal distance
Non linear (linear) dependence of the current in the high voltage (low
voltage) range observed is perfectly consistent with the presence of a
tunnel barrier in correspondence of the metallic CNT/movable junction
Applications:
Electron beam Induced deposition
CNT e- beam damaging ?
• Exposing medium regionofasuspendedCNT…
• I-V before (a) and after (b) the exposure…
• No variations observed (c).
No damaging effecton the CNT structure
(10 keV, 1 hour exposure)
Applications:
-1.0 -0.5 0.0 0.5 1.0
-8.0x10-6
-6.0x10-6
-4.0x10-6
-2.0x10-6
0.0
2.0x10-6
4.0x10-6
6.0x10-6
8.0x10-6
0min
5min
10min
15min
20min
Curr
ent
(A)
Voltage (V)
Rsat=120 kW >12.9 kW
Welding of CNTse- beam exposed area
• After the welding, single nanotube can be pulled out from the Ni surface ...
• ... contacting another CNT ...
• a stable CNT/CNT omhicjunction can be produced by EB nanowelding.
Applications:
M. Passacantando et al. Phys. Rev. B 76, 125415 (2007)
Applications:
CNT welded on AFM tip
I-V measure on CNTsMicromanipulator Kleindiek
Applications:
MWCNT/Sapphire
Sample A: TG=500 °C
Sample B: TG=750 °C
Applications:
Photoconductivity in defective carbon nanotubes sheets
under UV-Vis-NIR radiationPassacantando et al. Appl. Phys. Lett. 93, 051911 (2008)
Applications: PhotoconductivityPassacantando et al. Appl. Phys. Lett. 93, 051911 (2008)
Photocurrent (Iph=Ilight-Idark)
White Light illumination
Relatively large area samples show,
under white light illumination, a
wide-range linear behavior of the
photocurrent as a function of bias
voltage and optical power density
Applications: PhotoconductivityPassacantando et al. Appl. Phys. Lett. 93, 051911 (2008)
The spectral photoresponse has beendetermined in terms of thephotoconductance (G ) normalized to theincident photon flux, nph=λF/hc, as givenby:
G=Iph/(SVpolnph)
where c is the speed of light, h is thePlanck constant, and S is the illuminatedarea.
The spectral photoresponse of
all the samples increases with
increasing photon energy and is
strongly correlated to the
absorbance.
Field emission from a selectedmultiwall carbon nanotube
Applications:
We have shown that the emission phenomenon is very well described by a
series resistance modified Fowler–Nordheim model.
M. Passacantando et al., Nanotechnology 19 (2008) 395701
M. Passacantando et al., Carbon 45 (2007) 2957
Applications:
This is an original method to limit or
suppress the field emission current from a
single nanotube through the controlled and
selective deposition of carbonaceous
species on its apical region.
This result opens several perspectives for
the study of the field emission properties of
carbon nanotube arrays, enabling the
switching of selected single emitters, as
well as for technological applications in
which tunable nanosized emitters might be
needed.
SEM image of the field emission geometry
after a prolonged electron beam exposure
of the tip region.
Passacantando et al. Nanotechnology 19 (2008) 395701
Low (T=400 °C) temperature Growth
CNT / CopperCNT / Glass
Structural analysis: Raman Spectroscopy
Catania, 6th October 2010
G-band: crystallographic graphitic order
~ 1582 cm-1
D-band: structural defects ~ 1350 cm-1
RBM: radial breathing mode ~ 230 cm-1
D
G
D
G
λ=633 nm
750°C 750°C
Catania, 6th October 2010
λ=633 nm
Si-c
300 cm-1
277 cm-1
258 cm-1
247 cm-1
190 cm-1
RBM
Structural analysis: Raman Spectroscopy
Synthesis of graphene:
Chemical Vapour Deposition (CVD)
AcknowledgementsThe research staff of L’Aquila:
Prof. Sandro Santucci
Dr. Luca Lozzi
Dr. Fabio Bussolotti (Japan Advanced Institute of Science and Technology, Ishikawa)
Dr. Valentina Grossi (Post Doc position)
Collaborations:
Dr. Michelangelo Ambrosio – University of Napoli
Prof. Pasqualino Maddalena and his group – University of Napoli
Dr. Emanuela Esposito - CNR-ICIB – Napoli
Prof. Antonio Di Bartolomeo – University of Salerno
Prof. Maurizio De Crescenzi – University of Roma “Tor Vergata”
Prof. Gilles Martel – Université de Rouen – France
Financial support:
European Collaborative Project “S-five”.
GINT (Gruppo INFN per le Nano Tecnologie) program, funded by INFN.
SinPhoNIA program, funded by INFN.
Thanks!
Photosensor made of MWCNTs:
details of device fabrication
The devicePt electrodes
MWCNT film
Au strips
Multipin
sample holder
Rome, 17th September 2010
Photoelectric measurements
The sample holder has been connected
to external circuit for electrical measurements
(Keithley-236 electrometer controlled by LabView software)
Standard optical fiber:
light spot of ~0,8 mm2
Support for
external electrical contact
and horizontal movement
(step 0,625 mm)
Rome, 17th September 2010
Photoconductivity of MWCNT by white light
Pt
Si (100) n-type
Si3N4
Si3N4
Pt
V
A
+
-
-
+
I
V
I
V
Contacts: Ohmic – Schottky
ID: dark currentIL: current generated by a white light by a LED
Rome, 17th September 2010
Photoconductivity of MWCNT by white light
Vbias= -4 V
The photoconductivity measurements show that only the more defective
MWCNTs grown at 500 °C have a noticeable photosensitivity
Rome, 17th September 2010
Rome, 17th September 2010
Photoconductivity of MWCNT by LED light
Rome, 17th September 2010
IPh= IL - ID
The Iph has been normalized to the incident photon flux (nph):
Photoconductivity of MWCNT by LED light
where
The spectral photoresponse has been determined in terms of
the photoconductance (G) normalized
to the incident photon flux:
Photoconductance of MWCNT by LED light
Rome, 17th September 2010
phpol
ph
nSV
IG
Rome, 17th September 2010
Photoconductance of MWCNT by LED light
phpol
ph
nSV
IG
Application:
Photosensor made of MWCNTs
Catania, 6th October 2010
Standard optical fiber:
light spot of ~0,8 mm2
Support for
external electrical contact
and horizontal movement
(step 0,625 mm)
T= 500 °C and T= 750 °C
MWCNT
cross viewPt
Si (100) n-type
Si3N4
Si3N4
Pt
V
A
Catania, 6th October 2010
Application:
Photosensor made of MWCNTsID: dark currentIL: current generated by a white light by a LED
0 240 480 720 960 1200 1440
Time [min]
138
140
142
144
146
148
(a
) R
esis
tan
ce
[O
hm
]
Operating Temperature 165 °C
200
300
400
500
600
700
800
900
1000
(b)
Re
sis
tan
ce
[O
hm
]
(a)
(b)
10 25 50 75 100
ppb NO2
Appl. Phys. Lett., Vol. 82, 961 (2003)
First thermal
treatment
Second thermal
treatment
Resis
tance (W
)
Resis
tance (W
)
Time (min)
Growth over a Pt/Si3N4 Gas sensor deviceApplications:
Back Heater
Pt electrodes50 nm+10 nm Ta
Si3N4
Si3N4
30 m
Si
3 mm
5 mm
7,8 mm